Dendrelaphis cyanochloris, the Blue Bronzeback

blue bronzeback

A Blue Bronzeback from Huai Nam Dang National Park, Mae Taeng district, Chiang Mai

Genus Dendrelaphis (bronzebacks)

These are slender, arboreal, medium-sized snakes with large, prominent eyes. They are  active during the day and able to move swiftly. About twenty species are recorded in the East, from India through Southeast Asia into northern Australia. Seven species occur in Thailand, of which four also in the northern region.

Superficially, some of them resemble each other strongly and close inspection is needed to identify them. One of them, the Common Bronzeback (Dendrelaphis pictus), belongs to the most common snakes of the region.
They are non-venomous and harmless, but when annoyed many specimens will not hesitate to strike and bite. Because of their slender body, Thai call them ngu sai man, which means ‘curtain string snakes’. (1)
All species are oviparous, laying clutches of 6-15 eggs.

Blue Bronzeback (Dendrelaphis cyanochloris)

This snake is also known as Wall’s Bronzeback, named after the British herpetologist Frank Wall, who in 1921 was the first to describe it in India.

Thai name: ngu sai man fa khieo – งูสายม่านฟ้าเขียว

specimen Mae On

A Blue Bronzeback from Mae Takhrai National Park, Mae On district, Chiang Mai. Note the very slender body.

specimen Mae Taeng

Head and neck of a specimen from Huai Nam Dang National Park, Mae Taeng district, Chiang Mai. Note the much enlarged vertebral scales.

This handsome, very slender bronzeback resembles Dendrelaphis formosus from the South. It also somewhat resembles Cohn’s Bronzeback (Dendrelaphis striatus) from the South, but lacks the latter’s series of characteristic black, oblique bars on the anterior part of the body. Its morphology has a strong resemblance to that of a bronzeback known from Tak province, which probably is a new, thusfar undescribed species (see the article: Dendrelaphis spec., een bronzeback uit West-Thailand). The latter, however, can easily be distinghuised by its remarkable black saw-tooth pattern on the neck.

The Blue Bronzeback reaches a length of 140 cm. The back is covered with brownish bronze, smooth scales. The skin between the scales of the anterior part of the body is light blue or greenish blue and will be exposed when the body is expanded, as is the case in other bronzeback species. The name Blue Bronzeback refers to this phenomenon.

The head is moderately distinct from the neck and copper brown, similar in colour to the Common Bronzeback’s head. The iris of the eye is brown, the round pupil is black.

A conspicuous black streak runs from the loreal scale to the eye, and extends from the back of the eye onto the neck where peters out. (2).

There is no black or cream stripe on the flank, and the belly is uniformly yellowish or light green. The vertebral scales are much enlarged. The tongue is scarlet.

It feeds on lizards and frogs. A  female specimen, a roadkill from Umphang, contained a large agame and eleven eggs.

map

Map of Northern Thailand, black dots indicating where I came across the Blue Bronzeback.

habitat

Habitat of the species: evergreen forest mixed with pine in Huai Nam Dang National Park.

This bronzeback ranges from India to Peninsular Malaysia and  Singapore. The species is ‘mostly known from the northern provinces of the country and as far south as Phuket Island.’ (3)

In Northern Thailand these bronzebacks occur widely in evergreen mountain forests at elevations of over 800 metre asl. I came across them in Chiang Mai, Mae Hong Son, Lampang, Nan, Uttaradit, Phitsanulok and Tak provinces.

In a popular guidebook to Thailand’s snakes this rather common species was illustrated with a rather differently looking snake (4), giving rise to much confusion.

In southern Thailand it is sympatric with the Elegant Bronzeback (Dendrelaphis formosus) and Kopstein’s Bronzeback (D. kopsteini) and has been the subject of a long history of confusion, which finally has been settled by a comparative study of Vogel and Van Rooijen. (5) Dendrelaphis formosus has three black stripes on the posterior third of the body (all lacking in D. cyanochloris) and extremely large eyes (moderately large in D. cyanochloris). (6) However, the Elegant and Kopstein’s Bronzebacks have not been recorded in the North.

©SJON HAUSER: text, pictures and map.

References:

1. Merel J. Cox, 1991. The Snakes of Thailand and their Husbandry. Krieger, Malabar, Florida: 475.

2. Citing Cox: ‘A black stripe extends from the head through the neck onto the body, where it scatters and finally disappears.’  (Cox, 1991, ibid.: 150.)

3. Cox (1991), ibid.: 151; Patrick David, Merel J. Cox, Oliver S. G. Pauwels, Lawan Chanhome, and Kumthorn Thirakhup, 2004. Book Review. When a book review is not sufficient to say all: an in-depth analysis of a recent book on the snakes of Thailand, with an updated checklist of the snakes of the Kingdom. The Natural History Journal of Chulalongkorn University 4(1): 47-80, April 2004. (p. 60)

4. Merel J. Cox, Peter Paul van Dijk, Jarujin Nabhitabhata, and Kumthorn Thirakhupt,1998. A Photographic Guide to Snakes and other Reptiles of Thailand and South-East Asia. Asia Books, Bangkok: 70. The snake in the picture is from the Andaman Islands and is now considered a separate species, Dendrelaphis andamanensis. See: Gernot Vogel and Johan van Rooijen, 2011. Contributions to a Review of the Dendrelaphis pictus (Gmelin, 1789) Complex (Serpentes: Colubridae)—3. The Indian Forms, with the Description of a New Species from the Western Ghats. Journal of Herpetology 45 (1): 100-110 (p.104-106)

5. Gernot Vogel and Johan van Rooijen, 2007. A new species of Dendrelaphis (Serpentes: Colubridae) in Southeast Asia. Zootaxa 1394: 25-45.

6. Following the keys of Van Rooijen and Vogel (2008): Johan van Rooijen and Gernot Vogel, 2008. A new species of Dendrelaphis (Serpentes: Colubridae) from Java, Indonesia. The Raffles Bulletin of Zoology 56 (1): 189-197. (p. 193).